1. Field of the Invention
The invention relates generally to an electrophysiological (xe2x80x9cEPxe2x80x9d) catheter for providing energy to biological tissue within a biological site, and more particularly, to an EP catheter having a surface covering over its electrodes that prevents adhesion of coagulum forming blood platelets to the electrode surface while still allowing electrical conduction therethrough.
2. Description of the Related Art
The heart beat in a healthy human is controlled by the sinoatrial node (xe2x80x9cS-A nodexe2x80x9d) located in the wall of the right atrium. The S-A node generates electrical signal potentials that are transmitted through pathways of conductive heart tissue in the atrium to the atrioventricular node (xe2x80x9cA-V nodexe2x80x9d) which in turn transmits the electrical signals throughout the ventricle by means of the His and Purkinje conductive tissues. Improper growth of, or damage to, the conductive tissue in the heart can interfere with the passage of regular electrical signals from the S-A and A-V nodes. Electrical signal irregularities resulting from such interference can disturb the normal rhythm of the heart and cause an abnormal rhythmic condition referred to as xe2x80x9ccardiac arrhythmia.xe2x80x9d
While there are different treatments for cardiac arrhythmia, including the application of anti-arrhythmia drugs, in many cases ablation of the damaged tissue can restore the correct operation of the heart. Such ablation can be performed by percutaneous ablation, a procedure in which a catheter is percutaneously introduced into the patient and directed through an artery to the atrium or ventricle of the heart to perform single or multiple diagnostic, therapeutic, and/or surgical procedures. In such case, an ablation procedure is used to destroy the tissue causing the arrhythmia in an attempt to remove the electrical signal irregularities or create a conductive tissue block to restore normal heart beat or at least an improved heart beat. Successful ablation of the conductive tissue at the arrhythmia initiation site usually terminates the arrhythmia or at least moderates the heart rhythm to acceptable levels. A widely accepted treatment for arrhythmia involves the application of RF energy to the conductive tissue.
In the case of atrial fibrillation (xe2x80x9cAFxe2x80x9d), a procedure published by Cox et al. and known as the xe2x80x9cMaze procedurexe2x80x9d involves continuous atrial incisions to prevent atrial reentry and to allow sinus impulses to activate the entire myocardium. While this procedure has been found to be successful, it involves an intensely invasive approach. It is more desirable to accomplish the same result as the Maze procedure by use of a less invasive approach, such as through the use of an appropriate EP catheter system providing RF ablation therapy. In this therapy, transmural ablation lesions are formed in the atria to prevent atrial reentry and to allow sinus impulses to activate the entire myocardium.
During ablation, electrodes carried by an EP catheter are placed in intimate contact with the target endocardial tissue. RF energy is applied to the electrodes to raise the temperature of the target tissue to a non-viable state. In general, the temperature boundary between viable and non-viable tissue is approximately 48xc2x0 Celsius. Tissue heated to a temperature above 48xc2x0 C. becomes non-viable and defines the ablation volume. The objective is to elevate the tissue temperature, which is generally at 37xc2x0 C., fairly uniformly to an ablation temperature above 48xc2x0 C., while keeping both the temperature at the tissue surface and the temperature of the electrode below 100xc2x0 C. When the blood temperature reaches approximately 100xc2x0 C., coagulum generally occurs.
Blood coagulation is a major limitation/complication associated with RF ablation therapy. Coagulation can lead to thromboembolism and can also form an insulating layer around the electrode hindering further energy delivery required for ablation therapy. Heat appears to be a major factor in the formation of blood coagulum on a catheter electrode. During a typical RF energy ablation procedure using an EP catheter, on or more electrodes carried by the catheter are positioned such that a portion of the electrodes are in contact with the tissue being ablated while the remaining portion of the electrodes are in contact with blood. The RF energy applied during the procedure resistively heats the tissue which in turn heats the electrode through conduction. As blood stays in contact with the heated electrode, platelet activation occurs. This platelet activation appears to lead to coagulum formation.
Hence, those skilled in the art have recognized a need for providing a catheter with ablation electrodes that reduce or inhibit the formation of coagulum by preventing platelets and other substances from adhering to the electrode surface all without adversely affecting the electrical conductivity of the ablation electrode. The invention fulfills these needs and others.
Briefly, and in general terms, the invention is directed to an ablation catheter having a surface covering over its electrodes that prevents adhesion of blood platelets to the electrode surface while still allowing electrical conduction therethrough.
In a first aspect, the invention relates to a catheter for applying energy to biological tissue having biological fluid flowing thereby. The catheter includes a shaft having at least one electrode and a layer of a bio-compatible, non-electrically conductive porous structure covering at least a portion of the surface of the electrode. By incorporating a bio-compatible, non-electrically conductive porous structure coating or covering over the ablation electrode adhesion of blood platelets on the electrode surface is prevented or at least substantially minimized. As such, coagulum causing components of the blood cannot contact the electrode and coagulation cannot begin and therefore, not propagate.
In a detailed facet of the invention the bio-compatible, non-electrically conductive porous structure is a polymer structure and may include either one of a porous homopolymer or a porous copolymer. In a further detailed aspect, the porous homopolymer and the porous copolymer is based on anyone of polyurethanes, polyesters, polyolefins, polyamides, ionomers and fluoropolymers. In another detailed facet, the catheter further includes a layer of a metallic element covering the interiorwalls of the pores of the bio-compatible, non-electrically conductive porous structure. In yet another detailed aspect the catheter further includes a layer of a wetting agent covering the metallic element. In the absence of the metallic element, the interior walls of the bio-compatible, non-electrically conductive porous structure may be covered with a secondary surface such as a hydrophilic material or a plasma modified material. In another detailed aspect of the invention, the electrode includes a first surface portion and a second surface portion; the shaft is adapted to position the electrode adjacent the biological tissue such that the first surface portion contacts the tissue and the second surface portion remains in the fluid; and the layer of a bio-compatible, non-electrically conductive porous structure covers the first surface portion. In a further detailed aspect the catheter further comprises a layer of bio-compatible, non-electrically conductive structure covering the second surface portion.
In another aspect, the invention relates to a catheter for applying energy to biological tissue having biological fluid flowing thereby. The catheter includes a shaft having a curved distal-end region with an inner surface and an outer surface and a plurality of band electrodes positioned at the distal-end region of the shaft. The catheter further includes a surface covering including a first portion comprising a bio-compatible, non-electrically conductive porous structure covering a portion of each of the band electrodes.
In a detailed aspect of the invention, the surface covering further covers a portion of the shaft between band electrodes. In another detailed facet, each of the band electrodes includes a first surface portion that lies on the outer surface and a second surface portion that lies on the inner surface. The shaft is adapted to position the outer surface adjacent the biological tissue and the inner surface in the fluid. The first portion of the surface covering covers the first surface portion of each band electrode. In a further detailed aspect, the surface covering further includes a second portion comprising a bio-compatible, non-electrically conductive non-porous structure that covers the second surface portion of each band electrode. In further detailed aspects, the bio-compatible, non-electrically conductive structure comprises a porous polymer structure while the bio-compatible, non-electrically conductive structure comprises a non-porous polymer structure.
In another aspect, the invention relates to a catheter for applying energy to biological tissue having biological fluid flowing thereby that includes a shaft having a distal-end region carrying a plurality of band electrodes. The distal-end region defines a tissue-contacting surface and a fluid-contacting surface. A surface covering including a first portion comprising a bio-compatible, non-electrically conductive porous structure covers the portion of each of the band electrodes coincident with the tissue-contacting surface. In a detailed facet of the invention, the surface covering also includes a second portion comprising a bio-compatible, non-electrically conductive non-porous structure that covers the portion of each of the band electrodes coincident with the fluid-contacting surface.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings which illustrate by way of example the features of the invention.